The present application claims a priority from Japanese Patent Application No. 2015-127120, filed Jun. 24, 2015, which is incorporated herein by reference.
The present invention relates to an air cleaner incorporated in a stratified scavenging two-stroke internal combustion engine.
Two-stroke internal combustion engines are used as power sources for portable working machines such as a brush cutter, a chain saw, and a power blower.
U.S. Pat. No. 7,494,113 B2 discloses a stratified scavenging two-stroke internal combustion engine. A stratified scavenging engine, in a scavenging stroke, introduce air free of air-fuel mixture, namely fresh air, into a combustion chamber before introducing air-fuel mixture in a crankcase into the combustion chamber. The fresh air, which is introduced early in the scavenging stroke into the combustion chamber, is called “leading air”.
An engine disclosed in U.S. Pat. No. 7,494,113 B2 has an intake system having two passages. A first passage is an “air passage”. A second passage is an “air-fuel mixture passage”. The fresh air, or the leading air, is fed to an engine body through the air passage. Air-fuel mixture is fed to the crankcase of the engine body through the air-fuel mixture passage.
The intake system disclosed in U.S. Pat. No. 7,494,113 B2 is constituted by an air cleaner, a carburetor, and an intake member connecting the carburetor and the engine body. The intake member has a first partition wall extending continuously in the longitudinal direction. The intake member has an air passage and an air-fuel mixture passage that are made independent from each other by the first partition wall.
The carburetor disclosed in U.S. Pat. No. 7,494,113 B2 has a throttle valve and a choke valve. The throttle valve and the choke valve are each formed by a butterfly valve. The throttle valve and the choke valve are in their fully opened positions while the machine is working at full throttle.
The carburetor disclosed in U.S. Pat. No. 7,494,113 B2 has a second partition wall dividing an internal gas passage of the carburetor into two passages. When the throttle valve and the choke valve are in the fully opened positions, these two valves and the second partition wall divide the internal passage of the carburetor into the air passage and the air-fuel mixture passage.
In this way, while the machine is working at full-throttle operating condition, air that has been cleaned by the air cleaner is fed to the crankcase through the air-fuel mixture passage as well as to the engine body through the air passage. The carburetor has a fuel nozzle in the air-fuel mixture passage. Fuel is sucked out through the fuel nozzle by air passing through the air-fuel mixture passage, and air-fuel mixture, that is, a mixture of fuel and air is generated within the air-fuel mixture passage in the carburetor.
U.S. Pat. No. 7,494,113 B2 discloses two types of carburetors. First and second types of carburetors are different from each other in their partition walls. In the first type of carburetor, the partition wall is shaped to divide, together with a fully opened throttle valve and a fully opened choke valve, the gas passage in the carburetor into two passages (FIG. 3 in U.S. Pat. No. 7,494,113 B2). That is to say, an intake system provided with the first type of carburetor has an air passage and an air-fuel mixture passage that are independent from each other, while the engine is operating under high speed rotation.
In the second type of carburetor, the partition wall is shaped similarly to that of the first type of carburetor but has a window formed by cutting away a part of the partition wall (FIG. 4 in U.S. Pat. No. 7,494,113 B2). The air passage and the air-fuel mixture passage in the second type of carburetor are in communication to each other all the time via the window. In other words, an intake system provided with the second type of carburetor has a window communicating with the air passage and the air-fuel mixture passage. The air passage and the air-fuel mixture passage of the intake system extend from the air cleaner to the engine body. In an intake system provided with the second type of carburetor, the air passage and the air-fuel mixture passage are partly in communication with each other all the time via the window, or the opening portion, while the engine is operating under high speed rotation.
Two-stroke internal combustion engines including the stratified scavenging two-stroke internal combustion engine have a problem of air cleaner contamination caused by blow-back of fuel. The fuel blow-back problem is caused not only by blow-back of air-fuel mixture from the air-fuel mixture passage, but also by blow-back of air from the air passage. It is natural that this problem is caused in an engine having the second type of carburetor. The problem is also caused in an engine having the first type of carburetor during acceleration or deceleration, or at half throttle.
Japanese Patent Laid-Open No. 2009-185633 proposes a measure to prevent contamination of an element due to blown-back fuel by effectively using the characteristics of stratified scavenging two-stroke internal combustion engines. Specifically, Japanese Patent Laid-Open No. 2009-185633 proposes an air cleaner for a stratified scavenging two-stroke internal combustion engine.
The air cleaner disclosed in Japanese Patent Laid-Open No. 2009-185633 has a first inlet through which clean air cleaned by an element is sent to an air passage of a carburetor and a second inlet through which the clean air is sent to an air-fuel mixture passage of the carburetor. The first and second inlets are independent from each other.
The air cleaner disclosed in Japanese Patent Laid-Open No. 2009-185633 has a guide member guiding blown-back fresh air from the air passage to the second inlet. That is, the guide member is positioned adjacent to the first inlet and the second inlet and is shaped such that it guides the blown-back fresh air from the first inlet to the second inlet. Thus shaped guide member also functions to receive air-fuel mixture from the second inlet.
The guide member inhibits diffusion of blown-back fresh air from the first inlet and blown-back air-fuel mixture from the second inlet in the air cleaner.
The present invention aims to prevent contamination of an element in an air cleaner incorporated in a stratified scavenging two-stroke internal combustion engine.
The present invention further aims to improve the effect of preventing the contamination of the element in the air cleaner disclosed in Japanese Patent Laid-Open No. 2009-185633.
The present invention further aims to provide an air cleaner used in a stratified scavenging two-stroke internal combustion engine that prevents contamination of an element due to blow-back of fresh air or air-fuel mixture from an intake system air passage or an intake system air-fuel mixture passage.